The present invention relates to dusting devices, in particular dusting devices for dusting products.
The dusting of products to obtain a desired surface quality by means of a powder gas is known (see for example DE 38 19 203 A1). Through such dusting for example the surface of freshly printed products is prepared, so that they do not stick together when stacked. A further application is dusting of rubber as well as glass (the latter in particular in the production of laminated sheets).
A problem when dusting products is excess, unused powder. In order to carry it away the dusting devices generally have a suction device. This however cannot prevent powder adhering to the walls and top of a housing, which surrounds powder discharge nozzles. The dusting powder adhering to the walls and top can fall down in the form of clumps or flakes and fall onto the product being dusted and contaminate this as a result.
In order to overcome this problem today microporous plates are used for the walls and top of dusting devices, whereby the microporous plates are fed with compressed air from compressed air chambers on their outer side. In this way air at low speed continually escapes from the surfaces of the microporous walls, which prevents powder particles settling on the walls (see DE 196 48 227 A1).
These microporous walls fulfil their purpose satisfactorily, but consist of a special sintered plastic, which is very expensive.
An object of the invention is to find an economic solution to keep the powder away from the housing walls.
According to the present invention there is provided, a dusting device comprising:
a housing;
at least one powder gas delivery device which discharges a powder gas jet onto a surface of products moved in one conveyor direction; and
a suction device for unused powder gas, whereby at least one housing wall is permeable for an airstream;
in which at least one permeable housing wall has an air-permeable filter mat arrangement.
It has been found that air-permeable filter mats, which are considerably cheaper than the state of the art microporous plates, very satisfactorily fulfil the purpose of keeping powder away from the surface of the wall formed by them.
A further advantage in contrast to a dusting device with microporous plates consists in the fact that feeding with compressed air and the technical measures associated with this are not necessary, but that a normal fan is sufficient to move air through the filter mats.
If the product width in the transverse direction is great relative to the conveying direction, a number of fans can be used.
If only one wall or top of the device housing has filter mats, the airstream discharged by this preferably flows mainly parallel to the powder gas jet. Therefore powder rising to the top is effectively moved downwards or to the open end of the device housing and therefore into the vicinity of the suction device.
The filter mats are preferably held by mat holders formed as a grid. Thus as little space as possible is taken up by the mat holder so that a homogeneous airstream is produced.
It is advantageous if the permeable filter mats used according to the invention are fitted in the device so that they can be replaced, for example by removing them from the mat holders and replacing them with new ones. As a result it is possible, in the event of the pores of the filter mats possibly becoming blocked and the impaired function associated with this, to quickly take remedial action.
Therefore it is also preferable if the filter mat arrangement used according to the invention with individual walls includes a number of filter mats arranged directly next to each other so that replacement is easier.
Preferably the filter mats consist of a polyester material, more precisely polyester fibre. This material is very tough, for example moisture-proof to approx. 100% relative air humidity and temperature resistant to approx. 100xc2x0 C. The fibres are unbreakable and can to a certain extent be regenerated (beating, washing the filter mats is possible).
Preferred filter mats have a material thickness of 10-30 mm, preferably 15-20 mm, a weight per m2 of 150-200 g, preferably 180 g, and an initial pressure differential of 25-45 Pa, preferably 30-40 Pa and in particular approx. 33 Pa.
It is most preferable if the upper or top-housing wall and two lateral or even all four lateral housing walls in each case have a filter mat arrangement.
In this case all housing walls, which include a filter mat arrangement, are surrounded by a single interconnected or several separate air chambers.
Suction devices are preferably arranged on the lower end of the two longer lateral housing walls or those transversal to the product conveyor direction along the whole length of the walls. This enables excess powder to be efficiently sucked up.
Especially in the case where the lateral walls do not include a filter mat arrangement the suction device has a powder trapping wall, which can possibly collect powder falling from the lateral walls.
The suction device comprises a suction aperture, the size of which can be adjusted with a slide. Therefore the suction can be adapted to the dusting powder.
The air which is moved through the filter mat arrangement is preferably cleaned by a filter in order to prevent the filter mats being blocked from the rear.